Preservatives for wood and other cellulosic materials

ABSTRACT

PCT No. PCT/GB92/01427 Sec. 371 Date Apr. 4, 1994 Sec. 102(e) Date Apr. 4, 1994 PCT Filed Aug. 3, 1992 PCT Pub. No. WO93/02557 PCT Pub. Date Feb. 18, 1993The instant invention concerns a wood preservative composition comprising a synergistically effective amount of (a) a cuprammonium compound and (b) tebuconazole to preserve wood.

This invention relates to preservative for wood and other cellulosicmaterials.

The use of biocidal metal ions in wood preservation is well known. Thereare also many compounds containing a triazole group which are known topossess biocidal properties.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph correlating the additive and synergistic effects of aloading of hypothetical compound X relative to a loading of hypotheticalcompound Y. Points A and B are the toxic index values for biocidalcompounds Y and X respectively. The straight line between the two pointsillustrates the toxic index values which would be obtained if thebiocidal effects of compounds X and Y were merely additive.

FIG. 2 is a graph correlating the loading of tebuconazole (Kg/m³) andthe loading of copper (Kg/m³). The dotted line illustrates the expectedconcentration of cuprammonium compound and tebuconazole which would beneeded in a composition containing copper and tebuconazole at a weightratio of 25:1 if the performance of copper and tebuconazole were merelyadditive. The solid line illustrates the actual concentrations found tobe required.

FIG. 3 is a graph correlating the retention of copper (Kg/m³) and theretention of tebuconazole (Kg/m³). The line with broad dashesillustrates a theoretical line of effectiveness assuming that theperformance of copper and tebuconazole are merely additive. The linewith narrow dashes illustrates the actual line of effectiveness. Thesolid lines illustrate the ratio of cuprammonium compound totebuconazole.

FIG. 4 is a graph correlating the loading of tebuconazole (Kg/m³) andthe loading of copper (Kg/m³). The dotted line illustrates the expectedconcentrations of cuprammonium compound and tebuconazole at a weightratio of 25:1 if the performance of copper and tebuconazole were merelyadditive. The solid line illustrates the actual concentrations found tobe required.

FIG. 5 is a graph correlating the loading of propiconazole (Kg/m³) andthe loading of copper (Kg/m³). The dotted line illustrates the expectedconcentrations of cuprammonium compound and propiconazole at a weightratio of 25:1 if the performance of copper and propiconazole were merelyadditive. The solid line illustrates the actual concentrations found tobe required.

FIG. 6 is a graph correlating the loading of azaconazole (Kg/m³) and theloading of copper (Kg/m³). The dotted line illustrates the expectedconcentrations of cuprammonium compound and azaconazole at a weightratio of 25:1 if the performance of copper and azaconazole were merelyadditive. The solid line illustrates the actual concentrations found tobe required.

According to the present invention there are provided preservativecompositions comprising a biocidal metal compound and a fungicidalcompound containing a triazole group wherein the weight ratio of metalatom: fungicidal compound containing the triazole group is at least1:2.5; with the specific exceptions of (i) composition (a) whichcontains 1.320% by weight of sodium nitride, 1.190% by weight of coppersulphate. 5H₂ O, 0.400% by weight of boric acid, 0.625% by weight ofsodium heptonate, 0.390% by weight of sodium hydroxide, 0.012% by weightof tebuconazole, 0.391% by weight of surfactant blend in xylene and95.762% by weight of water and (ii) composition (b) which contains0.00025% by weight of a compound of formula: ##STR1## 0.025% by weightof a compound of formula ##STR2## 2.525% by weight of dimethylformamide,0.006313% by weight of alkylarylpolyglycolether the remainder beingwater.

We have found that compositions according to the invention possessadvantageous properties: in particular, it has been found that the metalcompound and the fungicidal compound containing the triazole group(hereinafter "the triazole compound") exhibit synergistic fungicidalactivity.

It will be understood that the metal compound may be present in a formsuch that metal ions are free in solution or may form part of a complex.Similarly, the triazole compound may be free in solution or may bepresent in the form of a salt or a complex. For example, the triazolecompound could be present in the form of a complex with part of thebiocidal metal ion.

The compositions according to the invention may be used to treatsubstrates such as wood or other cellulosic materials (such as cotton,hessian, rope and cordage). For convenience, the invention will bedescribed hereinafter with reference to the treatment of wood but itwill be appreciated that the other materials may be treated analogously.

The metal compound may be a compound of any biocidally active metalincluding copper, aluminum, manganese, iron, cobalt, nickel, zinc,silver, cadmium, tin, antimony, mercury, lead and bismuth. These may beeither used alone or in mixtures. The preferred metals are copper andzinc used alone, in combination with each other or with one or more ofthe metals listed previously. The most preferred metal is copper,particularly Cu (II) ion.

The triazole compound may be any compound which contains a triazolegroup and which possesses biocidal activity. Preferably the triazolecompound contains the triazole group. ##STR3##

Advantageously, the triazole compound is selected from compounds offormula (A): ##STR4## wherein R₁ represents a branched or straight chainC₁₋₅ alkyl group (e.g. t-butyl) and R₂ represents a phenyl groupoptionally substituted by one or more substituents selected from halogen(e.g. chlorine, fluorine or bromine) atoms or C₁₋₃ alkyl (e.g. methyl),C₁₋₃ alkoxy (e.g. methoxy) phenyl or nitro groups.

A particularly preferred compound of formula (A) is tebuconazole:

alpha-[2-(4-chlorophenyl)ethyl]-alpha(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol.

Alternatively, the triazole compound is advantageously selected fromcompounds of formula (B): ##STR5## wherein R₃ is as defined for R₂ aboveand R₄ represents a hydrogen atom or a branched or straight chain C₁₋₅alkyl group (e.g. n-propyl).

Particularly preferred compounds of formula (B) are: propiconazole(1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole) and azaconazole(1-[[2,4-dichlorophenyl)-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole).

Hexaconazole and difenaconazole are examples of further triazolecompounds which may be used in the compositions of the invention.

Compositions may contain more than one triazole compound for example,they may contain tebuconazole and propiconazole, or a mixture oftebuconazole, propiconazole and azaconazole.

We have found that the biocidal metal may advantageously be incorporatedinto the composition in the form of inorganic salts of the metal ione.g. in the form of the metal carbonate, sulphate, chloride, hydroxide,borate, fluoride or oxide. Alternatively the metal may be used in theform of the metal salt of simple organic compound e.g. in the form of asalt of a carboxylic acid such as a metal acetate. Thus, it has beenfound that the biocidal triazole compounds exhibit synergisticproperties when the metal ion is present in the form of such simplesalts, and it is not necessary to add the metal ion in the form of asalt of, or complex with, a larger more complex organic compound whichitself possesses biocidal properties.

The optimum weight ratio of metal ion to triazole compound variesdepending on the particular material or product to which the compositionis applied and the type of organism against which protection isrequired. Preferably the ratio by weight of metal to triazole compoundis less than 1000:1, e.g. no greater than 750:1. More preferably, theweight ratio of metal: triazole compound should be between 750:1 and1:1, particularly preferably between 500:1 and 2:1; most preferably thesaid ratio is between 50:1 and 5:1, especially about 25:1.

The concentration required for preservative treatment depends on theratio of metal to triazole compound selected, the metal chosen, themethod of treatment employed, the timber species, the level ofprotection required and the nature and quantity of any other biocidespresent. The levels necessary can be determined readily by one skilledin the art. In general, the level of metal required will be in the range0.01-5% and the level of triazole will be in the range 25 ppm to 1.0%.The preferred range for waterborne treatments is to have a metalconcentration of 0.1-5% and a triazole level of 50 ppm to 5000 ppm.

Compositions in accordance with the invention may if desiredadditionally contain nitrite ion. Alternatively, there can be advantagesassociated with the omission of nitrite ion from the compositions forexample, by leaving out nitrite ion the formation of certain noxiousgases is prevented.

The compositions of the present invention advantageously contain abiocidally active quaternary ammonium compound or tertiary amine salt.These compounds aid in the formation of emulsions of triazole compoundsin aqueous solutions of biocidal metal ion. Compositions containingquaternary ammonium compounds or tertiary amine salts can formmicro-emulsions which are particularly useful in the treatment oftimber. In addition, the presence of these compounds may mean thatadditional organic solvents are not necessary to solubilise the triazolecompound. Furthermore, the quaternary ammonium compounds and tertiaryamine salts are themselves biocidal and so they enhance the overallbiocidal activity of the composition. These compounds also improvepenetration of the biocidal metal ion and triazole compound into thetimber.

The composition in accordance with the invention may contain water assolvent, or an organic solvent or a mixture of solvents. Formulationscan be prepared as concentrates intended to be diluted at the treatmentfacility, or the formulations can be prepared in the form of dilutetreatment solutions. Optionally, separate solutions of biocidal metalion and triazole compound can be provided e.g. in the form of twoconcentrates intended to be mixed before or after dilution.

Suitable formulations may be prepared, for example, by preparing aqueoussolutions of metal ion complexes and subsequently adding an emulsifiedformulation of the triazole compound. Suitable complexing agents for themetal ion would be for example, polyphosphoric acids such astripolyphosphoric acid, ammonia, water soluble amines and alkanolaminescapable of complexing with biocidal cations; aminocarboxylic acids suchas glycine, glutamic acid, ethylenediaminetetra-acetic acid,hydroxyethyldiamine triacetic acid, nitrilotriacetic acid andN-dihydroxy ethylglycine; polymeric compounds which contain groupscapable of complexing with metallic cations such as polyacrylic acids;hydroxycarboxylic acids such as tartaric acid, citric acid, malic acid,lactic acid, hydroxybutyric acid, glycollic acid, gluconic acid andglucoheptonic acid; phosphonic acids such as nitrilotrimethylenephosphonic acid, ethylenediaminetetra (methylene phosphonic acid),hydroxyethylidene diphosphonic acid. Where the complexing agents areacidic in nature they may be employed either as free acids or as theiralkali metal or ammonium salts. These complexing agents may be usedeither alone or in combination with each other. Suitable surfactants fortriazole compounds include, for example, cationic, nonionic, anionic oramphoteric surfactants.

Suitable formulations can also be prepared, for example, by adding anemulsified formulation of the triazole compound to an aqueous solutionof a metal salt, such as copper sulphate or zinc acetate. At high ratiosof metal ion to azole, the solubility of the azole may be sufficient todisperse the azole in the formulation using a suitable co-solvent.

Alternatively, formulations can be prepared employing only organicsolvents. To prepare such formulations, a biocidal metal salt of acarboxylic acid (e.g. decanoic or octanoic acid) is prepared anddissolved in a suitable organic solvent to form a concentrate. Thetriazole compound can then be added directly to the concentrate or to asolution diluted with a suitable solvent such as an ester, alcohol,ester alcohol, aliphatic or aromatic hydrocarbon, glycol ether, glycolor ketone.

Concentrated formulations containing organic solvents can optionally bemixed with water to form an emulsion which can be stabilized withsurfactants if necessary.

Compositions in accordance with the invention can optionally containother additives conventionally employed in timber preservation such aswater repellents, color additives, viscosity modifiers or corrosioninhibitors.

The compositions of the invention may contain other organic compoundsincluding fungicides, insecticides and bacteriocides. Such organiccompounds include carboxylic acids such as naphthenic acids and branchedaliphatic acids and their metal salts such as copper and zincnaphthenate, phenols and substituted phenols such as orthophenyl phenoland its alkali metal or ammonia salts; polyhalogenated phenols such aspentachlorophenol or tribromophenol and their alkali metal or ammoniasalts; quaternary ammonium salts and tertiary amine salts such asdidecyl dimethyl ammonium chloride, octyl decyl dimethyl ammoniumchloride, dodecyl dimethyl benzyl ammonium chloride, dodecyl benzyltrimethyl ammonium chloride, dodecyl dimethyl amine acetate, dodecyldimethyl amine lactate, dodecyl dimethyl amine salicylate, didodecylmethyl amine chloride; isothiazolone derivatives such as4,5-dichloro-2-(n-octyl)-4-isothiazolin-3-one or2-methyl-4-isothiazolin- 3-one, 2n-octyl-4-isothiazolin-3-one andmixtures of those and other related compounds; sulphamide derivativessuch asN,N-dimethyl-N-phenyl-(N-fluorodichloro-methylthio)-sulphonamide,N,N-dimethyl-N-tolyl-N-(dichlorofluoro-methylthio)-sulphamide; azolessuch as imidazole; MBT (methylene-bis thiocyanate); IPBC(3-iodo-2-propanyl-butyl-carbamate); carbendazim and chlorothalonil;N-nitrosophenylhydroxylamine and N-nitroso cyclohexyl hydroxylamine,either as their metal salts or as metal chelates; pyrethroid typeinsecticides selected from the group consisting ofcyano-(4-fluoro-3-phenoxyphenyl)-methyl-3-(2,2-dichloroethenyl)-2,2-dimethyl-cyclopropanecarboxylate,(3-phenoxyphenyl)-methyl-3-(2,2-dichloroethyenyl)-2,2-dimethylcyclopropanecarboxylate,cyano-(3-phenoxyphenyl)-methyl- 2-(4-chlorophenyl)-3-methylbutyrate, andmixtures thereof; organo-phosphorous, carbamate and organochlorineinsecticides such as lindane.

Other biocidally active elements may also be present such as boron, inany form, for example boric acid, boron or boron esters and alsofluorides and silicafluorides.

Particularly preferred compositions in accordance with the inventioncomprise copper (II) ion, a triazole compound which is tebuconazole orpropiconazole, and an alkanolamine, as well as borate ion and/or aquaternary ammonium compound or a mixture of quaternary ammoniumcompounds.

According to a further aspect of the invention there is provided amethod of treating a substrate of the type hereinbefore defined whichcomprises applying to the substrate a composition as defined above. Alsowithin the scope of the invention is a method of treating a substrate ofthe type hereinbefore defined which comprises applying to the substratecomposition (b) as defined above.

The skilled man will be well acquainted with the various methods oftreating the substrates with aqueous solutions. For example, thecompositions according to the invention may be applied to wood bydipping, spraying, deluging, brushing and by vacuum and/or pressureimpregnation. Other types of substrate may be treated by analogousmethods.

The following non-limiting Examples further illustrate the invention.

EXAMPLES

The compositions of Examples 1 to 3 may be prepared by adding anemulsified formulation of the triazole compound to an aqueous solutionof a metal complex.

    ______________________________________                                                          % w/w                                                       ______________________________________                                        Example 1 A concentrate formulation; metal to azole ratio                     ______________________________________                                        25:1                                                                          Basic copper carbonate                                                                            10.9                                                      Monoethanolamine    23.1                                                      Boric acid          16.9                                                      Tebuconazole        0.24                                                      Xylene              3.76                                                      Process oil         4.00                                                      Anionic/non-ionic emulsifier                                                                      1.00                                                      Water               40.10                                                     ______________________________________                                        Example 2 A ready to use solution; metal to azole ratio                       ______________________________________                                        10:1                                                                          Copper sulphate pentahydrate                                                                      1.18                                                      Lactic acid         2.13                                                      Sodium nitrite      1.31                                                      Boric acid          0.79                                                      Ammonium hydroxide  0.57                                                      Tebuconazole        0.03                                                      Cypermethrin        0.05                                                      Methyl dioxitol     0.64                                                      Anionic/non-ionic emulsifier                                                                      0.08                                                      Water               93.22                                                     ______________________________________                                        Example 3 A ready to use solution; metal to azole ratio                       ______________________________________                                        5:1                                                                           Basic copper carbonate                                                                            0.55                                                      Ammonium hydroxide  0.65                                                      Ammonium bicarbonate                                                                              0.33                                                      Propiconazole       0.06                                                      Naphthenic acid     0.15                                                      Anionic/non-ionic emulsifiers                                                                     0.21                                                      Methyl dioxitol     0.48                                                      Water               97.624                                                    ______________________________________                                    

EXAMPLE 4

A ready to use solution; metal to azole ratio 5:1

The compositions of Examples 4 and 5 may be prepared by adding anemulsified formulation of the triazole compound to an aqueous solutionof the metal ion.

    ______________________________________                                                          % w/w                                                       ______________________________________                                        Copper acetate      0.43                                                      Zinc acetate        0.84                                                      Tebuconazole        0.06                                                      Ester alcohol       0.03                                                      2-ethyl hexanoic acid                                                                             0.03                                                      Process oil         0.03                                                      Anionic/non-ionic emulsifier                                                                      0.06                                                      Water               98.52                                                     ______________________________________                                        Example 5 A ready to use solution, metal to azole ratio                       ______________________________________                                        30:1                                                                          Copper sulphate pentahydrate                                                                      1.18                                                      Azaconazole         0.01                                                      Methyl dioxitol     0.08                                                      Anionic/non-ionic emulsifiers                                                                     0.01                                                      Water               98.72                                                     ______________________________________                                        Example 6 Two pack system                                                     ______________________________________                                        Pack A:                                                                       Copper carbonate    14.5                                                      Monoethanolamine    30.7                                                      Water               54.8                                                      Pack B:                                                                       Tebuconazole        10                                                        Ester glycol        50                                                        2-ethyl hexanoic acid                                                                             10                                                        Process oil         10                                                        Anionic/non-ionic emulsifiers                                                                     20                                                        ______________________________________                                    

The ratio of copper to Tebuconazole resulting from the mixing of Pack Aand Pack B can vary from 1:2.5 to 750:1 parts by weight.

The separate packs are intended to be mixed together at the treatmentfacility and diluted with water.

Examples 7 to 11 contain organic solvents.

    ______________________________________                                                        % w/w                                                         ______________________________________                                        Example 7 A concentrate                                                       Zinc versatate    15.0                                                        Tebuconazole      0.5                                                         Glycol ether      10.0                                                        White spirit      74.5                                                        Example 8 A concentrate                                                       Copper caprylate  25.0                                                        Tebuconazole      0.05                                                        Shellsol A        74.75                                                       Permethrin        0.2                                                         Example 9 A concentrate                                                       Copper acypetacs  15.0                                                        Hexylene glycol biborate                                                                        10.0                                                        Cypermethrin      0.1                                                         Tebuconazole      0.1                                                         White spirit      74.8                                                        Example 10 A concentrate                                                      Zinc octoate      50.0                                                        Azaconazole       1.0                                                         Glycol ether      49.0                                                        Example 11 A ready to use solution                                            Copper versatate  5.0                                                         Propiconazole     0.01                                                        Permethrin        0.1                                                         White spirit      94.89                                                       ______________________________________                                    

The compositions of Examples 12 and 13 each contain a biocidally activequaternary ammonium compound. These compounds stabilize the triazolecompound in the treatment solution obtained by diluting the concentratedcompositions.

    ______________________________________                                        Example 12 A concentrate                                                                          % w/w                                                     ______________________________________                                        Monoethanolamine      19.23                                                   Basic copper carbonate                                                                              7.27                                                    Benzalkonium chloride (50% active)                                                                  8.0                                                     Tebuconazole          0.8                                                     Boric acid            11.3                                                    ______________________________________                                    

Weight ratio Cu:benzalkonium chloride:Tebuconazole 5:5:1

EXAMPLE 12(a)

A concentrate was made having the same formulation as Example 12 exceptthat monoethanolamine was replaced by ethylenediamine.

    ______________________________________                                        Example 13 A concentrate                                                                         % w/w                                                      ______________________________________                                        Monoethanolamine     30.77                                                    Basic copper carbonate                                                                             14.50                                                    Didecyldimethylammonium methyl                                                                     8.0                                                      sulphate (50% active)                                                         Propiconazole        0.32                                                     ______________________________________                                    

Weight ratio Cu: Didecyldimethylammonium methyl sulphate: Propiconazole2:1:0.08

EXAMPLE 13(a)

A concentrate was made having the same formulation as Example 13 exceptthat monoethanolamine was replaced by diethanolamine.

Synergistic Action of Mixtures Formulated According to the Invention

The toxic limit value for a particular biocidal compound is theconcentration of the compound which is required to prevent degradation(defined as >3% mass loss) of a substrate by a target organism. Toxiclimits are normally expressed as two experimentally-determinedconcentrations that span the pass/fail point of the test. The toxicindex is the midpoint of these two values. Where a preservativecomposition contains two biocidal compounds at a particular ratio, thetoxic index is the estimated minimum concentration of each biociderequired for effective protection of the substrate from the targetorganism. In FIG. 1 of the accompanying drawings, points A and B are thetoxic index values for biocidal compounds Y and X respectively and thestraight line between these two points illustrates the toxic indexvalues which would be obtained if the biocidal effects of compounds Xand Y are merely additive. If, for any particular ratio of X:Y, thetoxic index value is found to be below the straight line (e.g. at pointC), then compounds X and Y are synergistic at that particular ratio.

A convenient method of assessing the synergistic properties of aformulation is to use a `synergistic index`. This may be defined as:##EQU1##

The theoretical toxic index may be calculated by interpolation to thetheoretical line of action. A SI of 1 indicates no synergism. As the SIincreases, so the degree of synergism also increases.

A) Compositions containing tebuconazole

(i) Fungicidal effect on basidiomycete

Fungicidal activity was measured according to the test method pr EN113.This method involves treating small wood blocks with the preservativecompounds and then exposing them to the decay fungi in a small testvessel. Using a range of treatment concentrations, estimation ofperformance is determined after a 12 week exposure period by measuringthe weight loss of the blocks. Average values for weight loss forreplicate samples allow the determination of an estimated concentrationor loading of preservative in the wood which will be effective againstthe target fungus. In order to demonstrate synergism, results have beenobtained using tebuconazole alone, a substituted cuprammonium compoundand then together as a mixture, the constituents of which are given asExample 1. The copper to tebuconazole ratio for this example was 25:1.All tests were carried out after cold water leaching according to themethod published as EN84. Although boron was included in theseformulations, this leaching procedure is sufficient to remove all of theboron. There is therefore no contribution of this active ingredient tooverall efficacy in the tests. Results are given in Tables 1 and 2 forthe individual active ingredients and Table 3 for the mixture.

                  TABLE 1                                                         ______________________________________                                        Toxic limit values for Tebuconazole as                                        determined by EN113 (kgm.sup.-3 active ingredient)                                         Toxic Limit                                                                           Toxic Index                                                           kgm.sup.-3                                                                            kgm.sup.-3                                               ______________________________________                                        P. placenta    0.3-0.5   0.4                                                  C. Versicolor  0.2-0.4   0.3                                                  C. puteana     0.05-0.2  0.125                                                ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Toxic limit values for substitute coprammonium                                compounds determined by EN113 (kgm.sup.-3 copper)                                          Toxic Limit                                                                           Toxic Index                                                           kgm.sup.-3                                                                            kgm.sup.-3                                               ______________________________________                                        P. placenta    >4.62     Estimated value 5.0                                  G. trabeum     >4.49     --                                                   C. puteana     3.1-5.4   4.25                                                 ______________________________________                                    

These results clearly indicate the differential performance betweentebuconazole and the cuprammonium compounds. For the most aggressivefungus (Poria placenta) about 0.4 kgm⁻³ Tebuconazole is required foreffectiveness whilst approximately 5.0 kgm⁻³ of copper is required toprevent decay.

Further results for tests using a 25:1 mixture of copper to tebuconazoleare given in Table 3. Poria placenta was used as this is the mostaggressive fungus in the full EN113 test towards these two compounds.

                  TABLE 3                                                         ______________________________________                                        Toxic limit values for a 25:1 copper:tebuconazole                             mixture as determined by EN113. (Toxic limit                                  values given as kgm.sup.-3 Cu)                                                             Toxic Limit                                                                           Toxic Index                                                           kgm.sup.-3 Cu                                                                         kgm.sup.-3 Cu                                            ______________________________________                                        P. placenta    1.4-2.2   1.8                                                  ______________________________________                                    

These results have been plotted in diagrammatic form in FIG. 2 of theaccompanying drawings.

In FIG. 2, the dotted line illustrates the expected concentration ofcuprammonium compound and tebuconazole which would be needed in acomposition containing copper and tebuconazole at a weight ratio of 25:1if the performance of copper and tebuconazole were merely additive (3.2kgm⁻³ copper and 0.13 kgm⁻³ tebuconazole). The solid line illustratesthe actual concentrations found to be required. These concentrations areconsiderably lower than expected (1.8 kgm⁻³ copper and 0.072 kgm⁻³tebuconazole), producing a synergistic index of 1.78.

ii) Fungicidal effect of various copper:tebuconazole ratios

The above tests have been extended to delineate the range of ratios overwhich synergism exists between cuprammonium compounds and tebuconazole.A shortened version of the test prEN113 was used: the duration of thetest was 6 weeks; the target fungus was C.puteana as the growth rate ofthis copper tolerant fungus is reliable in a six week exposure test. Allblocks were cold-water leached according to prEN84. The compositionstested were obtained by mixing the packs A and B described in Example 6to obtain the copper: Tebuconazole ratios shown in Table 4, which alsoshows the toxic and synergistic indices found at these ratios.

                  TABLE 4                                                         ______________________________________                                                              Theoretical                                                        Toxic Index                                                                              Toxic Index                                                                              Synergistic                                  Formulation                                                                              (kgm.sup.-3)                                                                             (kgm.sup.-5)                                                                             Index                                        ______________________________________                                        Tebuconazole                                                                             0.048   ai                                                         Cuprammonium                                                                             4.91    Cu                                                         compound                                                                        1:10     0.048   ai     0.048 ai   1.00                                      25:1      <0.48   Cu     0.95  Cu   >2.08                                     500:1     <1.90   Cu     4.10  Cu   >2.10                                    1000:1     4.34    Cu     4.40  Cu   1.01                                     ______________________________________                                         N.B. Ratios given as Copper:Tebuconazole                                      ai = active ingredient                                                   

These values clearly show the surprising differences in fungicidalactivity exhibited by different ratios of Cu:tebuconazole; they areshown in diagrammatic form in FIG. 3. Whereas at 1:10 and 1000:1 thefungicidal activity of Cu and tebuconazole are purely additive, at 25:1and 500:1 the formulations are significantly synergistic.

iii) Fungicidal effect against soft rot

The mixture used in the previous test was further tested in a fungalcellar test where activity against soft rot was assessed. Results fromthis test are particularly important in assessing the suitability ofwood preservatives for use in ground contact.

Small stakes of wood (15×3×100 mm) of Beech were exposed in unsterilesoil to nine-tenths of their length. The exposure period was six months.Leached samples were used. The strength loss was used as the maincriteria for assessment. 80% of residual strength was used as the levelat which toxic limits were determined.

Toxic thresholds on Beech against soft rot for individual components andmixtures after leaching are given below (in this table, the toxic limitand toxic index for the cuprammonium compound are given in kg of Cu perm³).

                  TABLE 5                                                         ______________________________________                                                       Toxic Limit                                                                            Toxic Index                                                          (kgm.sup.-3 active                                                                     (kgm.sup.-3 active                                                   ingredient)                                                                            ingredient)                                           ______________________________________                                        Tebucanozole     >9.09      >9.09                                             Cuprammonium compound                                                                          >8.44      >8.44                                             Copper:Tebuconazole 25:1                                                                       1.65-3.25  2.45                                              ______________________________________                                    

The interaction between the copper and tebuconazole for performance onBeech against soft rot is shown in FIG. 4 of the accompanying drawings.

In FIG. 4, the dotted line illustrates the expected concentrations ofcopper and tebuconazole needed in a composition containing copper andtebuconazole at a weight ratio of 25:1 if the performance of copper andtebuconazole were merely additive (>8.44 kgm⁻³ copper and >0.33 kgm⁻³tebuconazole). The solid line illustrates the actual concentrationsfound to be required. These concentrations are considerably lower thanexpected (2.44 kgm⁻³ copper and 0.01 kgm⁻³ tebuconazole).

These results show that the synergistic index of copper:tebuconazolecombined at a ratio of 25:1 is >3.58 when tested against soft rot fungi.

B) Compositions containing either propiconazole or Azaconazole

Tests to evaluate efficacy against basidiomycetes were carried out onPropiconazole and Azaconazole singly and in mixtures with copper usingratios within the scope of the invention. The tests were carried outaccording to both EN113 and the method published as IRG/WP/2329, andtoxic limits were identified as described above for the fungusConiophora puteana.

The toxic limits are given in the table below (in this table, the toxiclimit and toxic index for the duprammonium compound are given in kg ofCu per m³):

                  TABLE 6                                                         ______________________________________                                                       Toxic Limit  Toxic Index                                                      (kgm.sup.-3 total                                                                          (kgm.sup.-3 total                                 Active ingredient                                                                            active ingredient)                                                                         active ingredient)                                ______________________________________                                        Cuprammonium compound                                                                        3.1-5.4      4.25                                              Propiconazole  0.3-0.7      0.5                                               Azaconazole    0.7-1.3      1.0                                               Cu:Propiconazole 5:1                                                                         <0.504       <0.504                                            Cu:Azaconazole 5:1                                                                           1.008-2.04   1.52                                              ______________________________________                                    

The interaction between the propiconazole and copper is illustrated inFIG. 5; and that for azaconazole and copper is illustrated in FIG. 6.

In FIG. 5, the dotted line illustrates the expected concentrations ofcopper and propiconazole in a composition containing copper at a weightratio of 5:1 if the performance of copper and tebuconazole were merelyadditive (1.6. kgm⁻³ copper and 0.3 kgm⁻³ propiconazole). The solid lineillustrates the actual concentrations found to be required. Theseconcentrations are considerably lower than expected (<0.42 kgm⁻³ copperand <0.084 kgm⁻³ propiconazole). A synergistic of index of >3.77 wascalculated from these results for Cu:Propiconazole combined at a ratioof 5:1.

In FIG. 6, the dotted line illustrates the expected concentrations ofcopper and azaconazole needed in a composition containing copper at aweight ratio of 5:1 if the performance of copper and azaconazole weremerely additive (2.5 kgm⁻³ copper and 0.5 kgm⁻³ azaconazole). The solidline illustrates the actual concentrations found to be required. Theseconcentrations are considerably lower than expected (1.26 kgm⁻³ copperand 0.25 kgm⁻³ azaconazole).

These results suggest that copper: azaconazole mixtures combined of aratio of 5:1 are synergistic with a synergistic index of 1.97.

We claim:
 1. A wood preservative composition comprising asynergistically effective amount of (a) a cuprammonium compound and (b)tebuconazole to preserve wood.Iadd., wherein (a) and (b) are present ina ratio of between 500:1 and 5:1 by weight of copper ion totebuconazole.Iaddend.. .[.2. The wood preservative composition of claim1, wherein (a) and (b) are present in a ratio of between 500:1 and 2:1by weight..].3. The wood preservation composition of claim 1, wherein(a) and (b) are present in a ratio of between 5:1 and 50:1 by weight.Iadd.of copper ion to tebuconazole.Iaddend..
 4. The wood preservativecomposition of claim 1, wherein (a) and (b) are present in a ratio ofapproximately 25:1 by weight .Iadd.of copper ion totebuconazole.Iaddend..
 5. The wood preservative composition of claim 1wherein said cuprammonium compound is copper complexed with analkanolamine.